There are many prior switching power supply configurations for raising the level of a DC voltage from a relatively low level to a substantially higher level. For example, the Nagai et al., U.S. Pat. No. 3,828,239, discloses a high DC voltage generating circuit including a transistor 1 to alternately and successively connect and disconnect power to the primary winding 14a of a transformer 14. As shown in FIG. 4, two resonant circuits 19 and 21 are included in the primary circuitry of the voltage supply. Also, the output voltage from the secondary winding is applied to a voltage doubler rectifier circuit 16. A resonant frequency is chosen in conjunction with the switching frequency for the transistor 11 in order to cause a sinusoidal voltage to be developed across the secondary winding of the transformer 14. The relatively high amplitude sinusoidal voltage is passed through the voltage doubler rectifier circuit 16 connected to the output of the secondary winding 14b of transformer 14. When the primary winding is energized, the resonant circuits on the primary side generate a relatively high sinusoidal voltage, which is stepped up by the secondary winding 14b and applied to the voltage doubler rectifier to provide a substantially high DC voltage at output terminal 17. The required output voltage is in the order of 20,000 volts or more with a relatively low output current.
Rosa et al., U.S. Pat. No. 3,401,272, Rogers, U.S. Pat. No. 3,395,313, Angello, U.S. Pat. No. 3,381,201, and Gormley, U.S. Pat. No. 2,929,982 show other forms of switching power supplies.
Cambier, U.S. Pat. No. 4,377,842, discloses a flyback power supply including a switching transistor having a main current path connected in series with the primary winding of a transformer for charging the primary winding during turn on of the transistor, and causing discharge of the winding during turn off times of the transistor. As shown in FIG. 5, a damping circuit including the series connection of a resistor Rd and diode Sd, connected across the secondary of the flyback transformer provides for damping for oscillations caused by stray capacitances during switching of the transistor 14.
Simi et al., U.S. Pat. No. 4,495,554 discloses a switching power supply controlled by pulse width modulator 51 isolated from the output voltage by an isolation transformer 35. During the turn on time of a transistor 9 in the primary circuit, an inductor 5 is included as a storage element which ramps to a given current level during this time. When transistor 9 is turned off, some of the energy from the inductor 5 is transferred into the primary circuit of transformer 11. The inductor 5 incurs losses both during the turn on and turn off periods of the transistor 9, due to resistive and magnetic losses. The current driven into the primary winding during turn off of the transistor 9 is transferred to the secondary winding for charging capacitors 13 and 31. Over successive cycles of operation, the duty cycle of transistor 9 is controlled for obtaining a desired level of voltage across the output capacitor 31. Note that the secondary current at the turn off of transistor 9 is derived from the discharge of inductor 23 and current flow through diode 21, as a result of the negative voltage with respect to node C induced across the secondary winding at the time of turn off of transistor 9.
Davidson, U.S. Pat. No. 4,559,590 discloses a DC-DC converter including an inductor winding 21 in series with a capacitor 25, a primary winding 15, and a source of voltage 11. A first transistor switch 23 is connected between the common connection of the inductor 21 and capacitor 25 and the other end of the primary winding 15, for operating to shunt current away from this primary winding whenever the switch is turned on. A second switching transistor 26 is connected across the series combination of a capacitor 27 and another portion of the primary winding 16. A pulse width modulated controller is used to alternately turn on and off the two switching transistors. The combination of the inductor 21 and capacitor 25 in series with the primary winding 15 form a resonant circuit. Another resonant circuit is formed in the circuitry for secondary winding 17 via the parasitic inductor 19, capacitor 34, and capacitor 25 forming a series resonant circuit via inductive coupling between the secondary and primary windings. The switches 23 and 26 are alternately switched at a frequency and duty cycle that causes a sinusoidal voltage to be developed in the secondary 17 that is rectified to provide a DC output voltage across capacitor 13.
Nooijen et al., U.S. Pat. No. 4,593,346, discloses a switching power supply for providing two mutually independent output voltages across two secondary windings. The system relies on the transfer of voltage between the primary and secondary windings via resonant phenomenon, for providing sinusoidal currents in the secondary winding L2 (see FIG. 4). Series resonant circuitry is relied upon in each embodiment shown in this patent for transferring energy from the primary to the secondary windings of a power transformer.
Inoue, U.S. Pat. No. 4,659,894 discloses a switching power supply that includes the combination of a capacitor and diode in the secondary windings of a transformer. A capacitor of the power supply is remotely connected across a machining gap, and is connected to the remote power generator for charging the capacitor with pulses of a high-frequency electrical power. The capacitors are discharged across the machining gap for carrying out certain machining operations.
Geray et al., U.S. Pat. No. 4,660,134 discloses a DC-DC converter including the series connection of an inductor with a primary winding and capacitor between a source of voltage, a switching transistor connected across the combination of the primary winding capacitor, and full-wave bridge rectifier connected across the secondary winding of the transformer. The capacitor 28 is connected across interior nodes of the bridge rectifier, with a forward mode diode 26, connected within the bridge between the capacitor and one output diode 24. With reference to FIG. 2, during conduction of the chopper transistor 19, current flows through the secondary winding in the bridge diodes 24 and 25, through inductor 31, and output capacitor 32. With reference to FIG. 3, during non-conductive times of chopper transistor 19, current flows in the opposite direction through the secondary winding, through diode 22, into capacitor 28 (charging capacitor 28), through diode 23 and back to the secondary winding during an initial period of time after turn off of chopper transistor 19. The chopper transistor 19 is held non-conductive for a sufficient period of time that the charging current I.sub.1 diminishes to the point that capacitor 28 begins to discharge for the remainder of the cut-off period of transistor 19 through diode 26 and inductor 31 to the parallel combination of a load 33 and output capacitor 32.
Peterson et al., U.S. Pat. No. 4,688,158 discloses a flyback power supply system including a conventional diode capacitor combination in the secondary of the flyback transformer, and a sample-and-hold circuit in the feedback circuit from the output of the power supply to the control system for holding the level of the feedback signal, during times of energy storage in the primary of the transformer.
Ngo, U.S. Pat. No. 4,709,316 discloses a switching mode DC-to-DC convertor. As shown in FIG. 1, the converter includes a switching transistor 13 connected in series with the primary winding 11 of a transformer 10, for periodically connecting a DC source across the primary winding. A resonant capacitor 15 is connected to the secondary winding for forming a resonant circuit with the parasitic inductances from the secondary winding 12. A diode 16 is connected across the combination of the capacitor 15 and secondary winding 12. The converters are operated below the resonant frequency of the capacitor 15 and parasitic inductance of secondary winding 12, whereby the control means 25 operates to turn FET 13 off at times that the current flowing through the transistor is substantially zero or of a very low magnitude due to resonant phenomenon. When FET 13 is so turned off, current will flow from secondary winding 12 through diode 16, and capacitor 15, for charging capacitor 15. When FET 13 is turned on, diode 16 is back biased and capacitor 15 discharges into the filter circuit 17. Zero current switching in the transistors is obtained via the use of the resonant capacitor connected in series with the transformer secondary.
Rilly, U.S. Pat. No. 4,710,859 discloses a switching power supply of the DC-to-DC converter type, which as shown in FIG. 1 includes a peak-to-peak rectifier 45 connected across the secondary winding of a transformer 5. A forward diode 47 is conducting during the on-time of a switching transistor 9, to charge a first capacitor 46 to a voltage proportional to the level of the supply voltage V1. A flyback diode 48 is conductive during the off-time of transistor 9, and back biasing of a shunt diode 13, for discharging a capacitor 46 and charging another capacitor 49 to a voltage proportional to the peak-to-peak value V.sub.pp of the collector-to-emitter voltage V.sub.CE9 of the switching transistor 9. The turns ratio of the step-up transformer 5 determines the proportionality of the primary voltage relative to the secondary voltage.
Ariel, et al., U.S. Pat. No. 4,725,735, discloses a power supply that includes a free-running multivibrator for applying low pulse rate repetition square wave pulses to the primary of a transformer T1. The resulting voltage developed in the secondary T1 is passed through a voltage doubler circuit including capacitors C3, C4, C5, and diodes D4, D5, and D6 for providing a DC output voltage to charge capacitors C11 and C6.
Nakajima et al., U.S. Pat. No. 4,725,936 teaches a DC-DC converter including a resistive voltage divider for dividing down the level of the output voltage for providing a feedback signal to a pulse width modulated signal generator circuit 15, for controlling the pulse width of the control signal from the PWM 15. This control signal is applied to a switching transistor 12 connected in series with the primary of a transformer 11.